WO2011125140A1 - 接続材料半導体装置及びその製造方法 - Google Patents

接続材料半導体装置及びその製造方法 Download PDF

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Publication number
WO2011125140A1
WO2011125140A1 PCT/JP2010/006335 JP2010006335W WO2011125140A1 WO 2011125140 A1 WO2011125140 A1 WO 2011125140A1 JP 2010006335 W JP2010006335 W JP 2010006335W WO 2011125140 A1 WO2011125140 A1 WO 2011125140A1
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layer
connection
mass
content
connection material
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PCT/JP2010/006335
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English (en)
French (fr)
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靖 池田
知丈 東平
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株式会社日立製作所
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Publication of WO2011125140A1 publication Critical patent/WO2011125140A1/ja

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C13/00—Alloys based on tin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/24—Selection of soldering or welding materials proper
    • B23K35/26—Selection of soldering or welding materials proper with the principal constituent melting at less than 400 degrees C
    • B23K35/262—Sn as the principal constituent
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Definitions

  • the present invention relates to lead-free solder.
  • FIG. 1 shows a schematic diagram of a power module.
  • the power semiconductor element 6 is solder-connected to the substrate 3, and the substrate 3 on which the element 6 is mounted is connected to the support member 5 with the solder 4.
  • the element connecting portion becomes a high temperature of 125 to 175 ° C. Therefore, high lead solder having a melting point of 300 ° C. or higher is used for the power semiconductor element connecting portion. It has been.
  • high lead solder has a high lead content of 85% or more, and has a large environmental load.
  • the heat resistance of the Sn-based solder is determined by the reactivity between the main solder component Sn and the connected member. Therefore, it is important not to form an X-Sn intermetallic compound at the connection interface when connected.
  • As the method there is a method in which an element having a higher reactivity with the member than Sn is added to the solder. The inventor has confirmed that by adding Zn or Al as a main component of solder in addition to Sn, an X—Zn-based or X—Al-based intermetallic compound can be formed at the connection interface. However, as shown in FIG.
  • an X—Zn-based intermetallic compound such as Cu—Zn is easier to grow than a X—Sn-based intermetallic compound such as Cu—Sn and has low heat resistance.
  • an X—Al intermetallic compound such as Cu—Al is slower in growth than the Cu—Sn compound and can provide high heat resistance.
  • Al is the main component of solder
  • an Al oxide film is formed on the solder surface, which greatly impairs wettability during connection.
  • the Al oxide film is extremely stable in the temperature range of 250 to 400 ° C. at which solder connection is performed, and does not get wet to the connected material unless a very strong flux that mechanically breaks the film is used.
  • FIG. 4 is a Zn—Al binary phase diagram. Since the Zn—Al system is an alloy system having a wide solid solution region, Zn is very easily dissolved in Al. Therefore, when the clad material is melted, Zn and Al are blended and alloyed without separation, and a good connection state is obtained. On the other hand, Sn and Al are alloy systems having almost no solid solution region, as can be seen from the Sn—Al binary phase diagram of FIG. For this reason, even if connection is attempted, Sn11 in which Al12 is melted is repelled as shown in FIG.
  • the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a connection material that can secure wettability, has high heat resistance, and is light even if Al is contained. .
  • the present invention includes a Sn—Al-based alloy layer having an Al content of 40 mass% or less and a Sn layer provided on the outermost surface of the alloy layer. Provide material.
  • the Sn layer is clad on the outermost layer of an alloy containing Sn and Al as main components, so that wettability can be ensured, heat resistance is high, and a semiconductor device using a lightweight connection material and connection material Can be obtained.
  • FIG. 3 is a cross-sectional view of an Sn—Ag solder connection interface after being held at a high temperature. It is a figure which shows the growth thickness of various intermetallic compounds in 150 degreeC.
  • FIG. 4 is a Zn—Al binary phase diagram. It is a Sn-Al binary system phase diagram. It is a figure which shows typically the condition when the material which clad Sn on the outermost layer of Al is heated. It is sectional drawing which shows the connection material of this invention typically. It is sectional drawing which shows the connection mechanism of this invention typically. It is sectional drawing of the interface connected with the connection material of this invention. It is sectional drawing of the interface connected with the connection material of this invention. It is sectional drawing of the interface connected with the connection material of this invention. It is sectional drawing of the interface connected with the connection material of this invention. It is sectional drawing of the interface connected with the connection material of this invention.
  • the bonding material of the present invention comprises an Sn—Al based alloy layer 13 having an Al content of 40 mass% or less and an Sn based layer 11a provided on the outermost surface of the alloy layer.
  • the Sn—Al alloy layer 13 is shown as being divided into an Sn component 11b and an Al component 12 in the drawing, but in reality, it is a substantially uniform Sn—Al alloy.
  • the Sn-Al layers 13 are provided on the upper and lower surfaces of the Sn-Al-based alloy 13 having an Al content of 40 mass% or less by cold or hot clad rolling or pressure forming.
  • the Al oxide film (not shown) existing on the surface of the alloy layer 13 can be broken.
  • the nascent surface exposed by breaking the Al oxide film is metallically joined to the nascent surface of the Sn-based layer 11a whose surface oxide film is also torn. Since the center of the connecting material is the Sn—Al based alloy, the Sn component 11b of the Sn—Al based alloy layer 13 and the Sn component of the Sn based layer 11a are integrated when melted at the time of connection. A good connection can be made without such separation.
  • the Sn-based layer 11 has been deposited on the surface of the Al layer 12.
  • FIG. 8 is a cross section of a connection portion when the semiconductor element 1 is connected to the substrate 3 with the connection material of the present invention.
  • the Sn-Al alloy layer 13 and the Sn-based layer 11a were separated, but after the connection, the whole was a substantially uniform Sn-Al alloy.
  • the amount of Al component present on the surface of the Sn—Al based alloy is too large, so that it separates from the Sn based alloy layer on the surface. .
  • the Al content of the Sn—Al based alloy layer is 10 mass% or more, that is, 10 to 40 mass%.
  • an Al—X compound necessary for obtaining heat resistance can be formed at the connection interface under a wide range of connection conditions.
  • the Sn—Al-based layer alloy layer 13 melts with the Sn-based layer 11a, the proportion of Al decreases, but the thickness of the Sn-based layer 11a is equal to or less than the thickness of the Sn—Al-based alloy layer 13 even when both sides are combined.
  • the variation of the Al content at the time of connection is so small that it does not have to be taken into consideration.
  • the Sn-based layer 11a may be thin because it reduces the influence of the oxide film of the Sn—Al alloy layer 13, and it is preferable that the Sn-based layer 11a be not excessively thick in order to reduce composition fluctuations during connection.
  • FIG. 9 is a schematic view of a connection interface when the connection material of the present invention is connected to a Cu strip member.
  • a Cu—Al compound 21 is formed on the Cu 14.
  • FIG. 10 is a schematic diagram of the interface when the Ni-plated Cu member is connected with the connecting material of the present invention.
  • a Ni—Al compound 22 is formed on the Ni plating 15.
  • FIG. 11 shows a case where Cu strip members are connected with a connection material having an Al content of less than 10 mass% under the same connection conditions.
  • the Cu—Al compound 21 is liberated from the connection interface, and the Cu—Sn compound 23 is generated at the connection interface. This is because the Cu—Al compound 21 is formed at the early stage of connection because there is a large amount of Al that can be supplied to the connection interface. However, as the connection progresses, the Al that forms the compound is insufficient, so convection during solder connection, etc. This is because the Cu—Al compound 21 is released from the interface.
  • connection material having an Al content of less than 10 mass% when a connection material having an Al content of less than 10 mass% is used, adjustments are made such as shortening the connection conditions and lowering the connection temperature in order to obtain a connection interface having an Al—X compound with high heat resistance. Indicates that it is necessary. Therefore, by setting the Al content to 10 mass% or more, it is possible to obtain a connection material corresponding to a wide range of connection conditions. Further, by setting the Al content to 10 to 40% by mass, the connection material can be reduced in weight by 15% to 40% with respect to the general Sn-Ag solder used so far.
  • the Sn—Al based alloy layer 13 is Sn-10 to 40 Al mass%.
  • connection material is softer.
  • the connection material be softer.
  • the Sn—Al-based alloy layer 13 contains 0.01 to 9 mass% of Zn.
  • the solidus temperature of the solder can lower it to about 200 ° C. at the maximum.
  • the solidus temperature is about 30 ° C. lower than the solidus temperature of about 230 ° C., so that residual stress caused by cooling after connection can be reduced.
  • the Sn—Al—Zn ternary system is an alloy system that does not form a fragile intermetallic compound, the reliability of the connecting portion can be ensured. Even when Zn is contained as a main component, an Al—X intermetallic compound can be formed at the connection interface. When Zn content rate becomes higher than 9 mass%, there exists a possibility that Zn may impair the wettability and moisture resistance of a connection material.
  • the Sn—Al-based alloy layer 13 contains 0.01 to 7 mass% of In.
  • the Sn content of the Sn-based layer 11a is 95-100 mass%.
  • clad rolling or pressure forming can be performed without causing cracks or the like on the surface, and a Sn—Al based alloy layer and good metal bonding can be obtained. Since the Sn layer 11a on the surface needs to be formed thinner than the central Sn—Al alloy layer 13, higher workability is desired.
  • the second element having a content of more than 5 mass% is present in Sn, precipitates may be precipitated in Sn or may be dissolved in Sn, thereby reducing workability.
  • the Sn-Al-based alloy layer 13 When a large amount of the third element such as Zn or In described above is present in the central Sn—Al-based alloy layer 13, even if the workability is reduced and fractured during rolling, the Sn-Al-based alloy layer 13 is sealed with the outermost Sn-based layer 11 a. Therefore, the connectivity is not particularly affected.
  • the outermost Sn-based layer 11a is torn, the portion where the Al oxide film on the surface of the Sn—Al-based alloy layer 13 is destroyed by processing is oxidized again to form Al oxide, There is a possibility of impairing wettability.
  • the ratio of the Al oxide remaining interface existing at the entire interface between the Sn—Al-based alloy layer 13 and the Sn-based layer 11a is 25% or less.
  • the ratio of the Al oxide remaining interface existing at the entire interface between the Sn—Al-based alloy layer 13 and the Sn-based layer 11a is 25% or less, so that the connection can be made without impairing the wettability.
  • the amount of processing at the time of fabricating the connection material is small, even if the Al oxide film on the surface of the Sn—Al alloy 13 in the center is torn, the torn film remains at the interface. This prevents metal bonding of the Sn-based layer 11a on the surface.
  • the ratio of the Al oxide remaining interface is more than 25%, approximately 20% of the connected portion is not connected due to non-wetting and voids.
  • the Sn-based alloy foil be stacked on top and bottom of the Sn-Al-based alloy foil and clad rolled or pressure-formed at a final processing degree of 80% or more.
  • the final degree of processing is an index indicating how much the material thickness before rolling and pressure forming is processed as a connecting material.
  • the final processing degree is expressed as 0%, and when the thickness becomes 1/10, the final processing degree is expressed as 90%.
  • the lower the final processing degree the higher the unconnected ratio in the connecting material.
  • This unconnected portion causes unwetting and voids when a member is connected as a connection material.
  • the Sn content of the solder connection portion between the semiconductor element and the substrate is 60 to 90 mass% and the Al content is 10 to 40 mass%.
  • a lightweight semiconductor device having high heat resistance can be obtained.
  • Sn and Al as main components, a connection without a brittle intermetallic compound can be made in the solder connection portion.
  • Sn is less than 60%, the softness of the connection portion is lowered, and sufficient stress buffering cannot be performed when thermal stress is generated.
  • the Sn content is higher than 90%, the Al content is less than 10 mass%, so that it is difficult to form an Al—X compound that suppresses the interface reaction at a high temperature of 150 ° C. or higher.
  • Al content rate is higher than 40 mass%, it cannot form with the connection material of this invention.
  • Example 1-20 An example in which the present invention is applied to a power semiconductor module will be described below.
  • a clad material 2 having a thickness of 140 ⁇ m and a Sn-Al alloy layer of 20 ⁇ m as the outermost layer and a Sn—Al-based alloy layer of 100 ⁇ m as the center layer as shown in Table 1 was prepared. First, Al and Sn are heated and melted at the ratios shown in Table 1 to create a Sn—Al based alloy layer, Sn layers are provided on both sides of the Sn—Al based alloy layer, and cladding is performed to perform cladding. Material 2 was created.
  • the prepared clad material 2 is placed on the substrate 3, and 10 mm ⁇ 10 mm.
  • Power semiconductor element 6 is laminated, and a weight is placed on the element.
  • the element-attached substrate on which wire bonding 1 has been performed is connected to the support member 5 with a 200 ⁇ m-thick Sn—Ag solder, the case is attached, gel is injected around the connection portion, and cured, as shown in FIG. A semiconductor device was manufactured. Except for the clad material 2, it is the same as the conventional semiconductor device.
  • Table 1 shows the results of investigating the specific gravity of the element connection material used in this semiconductor device connection step with respect to Sn, the connection area of the element connection portion, and the state of void formation in the connection portion when the semiconductor device is held at 175 ° C. for 1000 hours.
  • the element connection area the case where the connection area was 90% or more with respect to the element area was marked with ⁇ , and the case where the connection area was less than 90% was marked with x.
  • the holding at 175 ° C. for 1000 h the cross section of the connection interface was observed after holding for 1000 h.
  • connection area in any of the examples, a connection area of 90% or more with respect to the element area was obtained.
  • the void formation state of the connection portion after 175 ° C. for 1000 hours was confirmed, no void was formed in the connection portion in any of the examples. From the above, it has been clarified that wetting can be secured, heat resistance is high, and weight can be reduced by using the present invention.
  • a 150 ⁇ m thick Sn-3.5Ag or Sn-0.7Cu solder foil was placed on the substrate, and 10 mm ⁇ 10 mm.
  • the power semiconductor element was placed on the element, and a weight was placed on the element, in an H 2 reducing atmosphere at 300 ° C. for 5 min. Connected.
  • the element-attached substrate on which wire bonding 1 was performed was connected to the support member 5 with a 200 ⁇ m-thick Sn—Ag-based solder, a case was attached, a gel was injected around the connection portion, and cured to produce a semiconductor device.
  • connection area was less than 90% as shown in Table 2.
  • Comparative Example 4 there was almost no wet location. Since a good connection could not be obtained, heat resistance by holding at 175 ° C. for 1000 hours could not be carried out.
  • connection material for connecting the semiconductor element and the substrate has been described.
  • connection target is not limited to this, and other members such as connection terminals and leads may be used.

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Abstract

　パワーモジュールの大容量化に伴う素子接続部の温度上昇に伴い、濡れ性がよく、高耐熱な鉛フリーの接続材料が必要となっていた。　そこで、Ｓｎ１１ｂとＡｌ１２を主成分とする合金箔１３でありＡｌ含有率が４０ｍａｓｓ％以下の合金箔１３の最表層にＳｎ系層１１ａをクラッドまたは加圧成形して、合金表層の酸化膜を除去する。このときに、合金箔のＡｌ含有率を４０ｍａｓｓ％以下とする。これにより、ＳｎとＡｌの分離を抑えて、濡れ性が確保でき、耐熱性が高く、軽量な接続材料および接続ができる。

Description

接続材料半導体装置及びその製造方法
　本発明は、鉛フリーはんだに関するものである。
　パワーモジュールは、家電、ハイブリッド自動車等の電力制御に用いられている。インバータ駆動による省エネルギー化が可能であるため、近年、需要が増大している。図１にパワーモジュールの模式図を示す。パワー半導体素子６が基板３にはんだ接続され、素子６を搭載した基板３が支持部材５にはんだ４で接続される。ワイヤボンディング１を通じて数十から数百アンペアの電流を通電することで、素子接続部が１２５から１７５℃の高温となるため、パワー半導体素子接続部には融点が３００℃以上の高鉛はんだが使用されてきた。ただし、高鉛はんだは、鉛含有率が８５％以上と高く、環境負荷が大きい。そのため、使用時の素子接続部温度が低い製品から、高鉛はんだからＳｎ－Ａｇ系はんだ等に置き換えられ、鉛フリー化が進んでいる。しかしながら、一般的に使用されるＳｎ－Ａｇ系はんだの場合、１５０℃以上の高温下ではんだ主成分のＳｎと接続部材との間で反応が進み、図２のような空隙１０１が接続界面に生じて劣化する。そのため、接続部温度が１５０℃より高温となるパワーモジュールに対応できる鉛フリーはんだが必要になっていた。
　Ｓｎ系はんだの耐熱性は、はんだ主成分のＳｎと被接続部材間の反応性によって決まる。そのため、接続した際に接続界面にＸ－Ｓｎ系の金属間化合物を形成させないことが重要となる。その方法として、Ｓｎ以上に部材との反応性の高い元素をはんだ中に添加する方法が挙げられる。本発明者は、Ｓｎ以外にはんだの主成分としてにＺｎもしくはＡｌを添加することで、接続界面にＸ－Ｚｎ系、Ｘ－Ａｌ系の金属間化合物を形成できることを確認した。ただし、図３のようにＣｕ－ＺｎといったＸ－Ｚｎ系金属間化合物はＣｕ－ＳｎといったＸ－Ｓｎ系金属間化合物に比べて成長しやすく、耐熱性が低い。一方、Ｃｕ－ＡｌといったＸ－Ａｌ系金属間化合物は、Ｃｕ－Ｓｎ化合物に比べて成長が遅く高い耐熱性が得られることを確認している。ただし、Ａｌをはんだ主成分とした場合、はんだ表面にＡｌ酸化物の膜が形成され、これが接続時の濡れ性を大きく阻害する。Ａｌ酸化物の膜は、はんだ接続を行う２５０から４００℃の温度域で極めて安定であり、機械的に膜を破る、非常に強いフラックスを用いなければ被接続材に濡らすことがない。パワーモジュールの組立では、減圧してボイド低減するためにバッチ式の炉を用いることが多いため、スクラブ等の機械的な方法で酸化膜を破ることが難しい。また、フラックスを使用した場合、揮発成分がボイド生成原因となる可能性があるため、フラックスの使用も困難である。そのため、Ａｌを主成分とした場合にも材料自身で濡れを確保することが要求されている。Ａｌを主成分とする接続材料のＡｌ酸化膜による濡れ性阻害を回避する手段として特許文献１の方法がある。Ｚｎ－Ａｌ合金の濡れ性を改善するために、Ａｌ箔表面にＺｎをクラッドしている。クラッドの際に、圧延等の加工でＡｌが大変形するため、表面のＡｌ酸化膜が破れる。破れたＡｌ酸化膜はそのままの状態を維持するため、接続時に良好な濡れを確保することができる。
特開２００８－１２６２７２号公報
　しかしながら、上記特許文献１の方法を用いて、Ａｌの表面にＳｎをクラッドした場合、良好な接続を得ることはできなかった。図４は、Ｚｎ－Ａｌの２元系状態図である。Ｚｎ－Ａｌ系は広い固溶域を持つ合金系であるため、ＺｎがＡｌ中に極めて固溶しやすい。そのため、クラッド材が溶融した際にＺｎとＡｌは分離することなく馴染んで合金化し良好な接続状態が得られる。一方、ＳｎとＡｌの場合、図５のＳｎ－Ａｌ２元系状態図から分かるように、ほとんど固溶域を持たない合金系である。そのため、接続しようとしても図６のようにＡｌ１２が溶融したＳｎ１１をはじいてしまい、良好な接続ができない。
　本発明は、上記のような問題を解決するためになされたものであり、Ａｌを含んでいても、濡れ性が確保でき、耐熱性が高く、軽量な接続材料を提供することを目的としている。
　本願発明は、上記課題を解決するために、Ａｌ含有率が４０ｍａｓｓ％以下のＳｎ－Ａｌ系合金層と、前記合金層の最表面に設けられたＳｎ層とを備えたことを特徴とする接続材料を提供する。
　本発明によれば、ＳｎとＡｌを主成分とする合金の最表層にＳｎ層をクラッドすることにより、濡れ性が確保でき、耐熱性が高く、軽量な接続材料および接続材料を用いた半導体装置を得ることができる。
パワーモジュールの断面を模式的に示した図である。 高温保持した後のＳｎ－Ａｇ系はんだ接続界面の断面図である。 １５０℃における各種金属間化合物の成長厚さを示す図である。 Ｚｎ－Ａｌ２元系状態図である。 Ｓｎ－Ａｌ２元系状態図である。 Ａｌの最表層にＳｎをクラッドした材料を加熱したときの状況を模式的に示す図である。 本発明の接続材料を模式的に示す断面図である。 本発明の接続機構を模式的に示す断面図である。 本発明の接続材料で接続した界面の断面図である。 本発明の接続材料で接続した界面の断面図である。 本発明の接続材料で接続した界面の断面図である。
　本願発明の接合材料は、図７に示すように、Ａｌ含有率が４０ｍａｓｓ％以下のＳｎ－Ａｌ系合金層１３と、合金層の最表面に設けられたＳｎ系層１１ａとからなる。便宜上、図面ではＳｎ－Ａｌ合金層１３をＳｎ成分１１ｂとＡｌ成分１２に分けて記載しているが、実際にはほぼ均一なＳｎ－Ａｌ合金となっている。
　これによって、Ａｌ含有率が４０ｍａｓｓ％以下のＳｎ－Ａｌ系合金１３の上下面にＳｎ系層１１を、冷間もしくは熱間のクラッド圧延や加圧成形によって設けることで、加工前にＳｎ－Ａｌ系合金層１３の表面に存在していたＡｌ酸化物の膜（図示せず）を破ることができる。Ａｌ酸化物の膜が破れることで露出した新生面は、同じく表面の酸化膜が破れたＳｎ系層１１ａの新生面と金属的に接合される。この接続材料の中心がＳｎ－Ａｌ系合金であるため、接続時に溶融した際にＳｎ－Ａｌ系合金層１３のＳｎ成分１１ｂとＳｎ系層１１ａのＳｎ成分が一体化することで、図６のような分離を起こすことなく、良好な接続ができる。図６では、Ａｌ層１２の表面にＳｎ系層１１が析出してしまっている。
　図８は、本発明の接続材料で半導体素子１を基板３に接続したときの接続部断面である。接続前はＳｎ－Ａｌ系合金層１３とＳｎ系層１１ａとに分かれていたが、接続後は全体がほぼ均一なＳｎ－Ａｌ合金となっている。Ａｌ含有率が４０ｍａｓｓ％より高いＳｎ－Ａｌ系合金を用いた接続材料の場合、Ｓｎ－Ａｌ系合金表面に存在するＡｌ成分の量が多すぎるため、表面のＳｎ系合金層と分離してしまう。
　Ｓｎ－Ａｌ系合金層のＡｌ含有率が１０ｍａｓｓ％以上、すなわち１０～４０ｍａｓｓ％であることが望ましい。Ａｌ含有率１０ｍａｓｓ％以上にすることで、幅広い接続条件において、耐熱性を得るために必要なＡｌ－Ｘ系化合物を接続界面に形成することができる。ここで、Ｓｎ－Ａｌ系層合金層１３がＳｎ系層１１ａと溶融するとＡｌの割合が減少するが、Ｓｎ系層１１ａの厚さは両面あわせてもＳｎ－Ａｌ系合金層１３の厚さ以下とし、接続時のＡｌ含有率の変動は考慮しなくてよいほど小さいものとする。Ｓｎ系層１１ａは、Ｓｎ－Ａｌ合金層１３の酸化膜の影響を小さくするためにあるので薄くてよく、また、接続時の組成変動を少なくするために余分に厚くしないほうがよい。
　図９はＣｕむく部材に本発明の接続材料を接続したときの接続界面の模式図である。Ｃｕ１４の上にＣｕ－Ａｌ化合物２１が形成している。図１０は、ＮｉめっきをしたＣｕ部材を本発明の接続材料で接続したときの界面の模式図である。Ｎｉめっき１５上にＮｉ－Ａｌ化合物２２が形成している。
　一方、図１１は、同じ接続条件において、Ａｌ含有率１０ｍａｓｓ％未満の接続材料でＣｕむく部材を接続した場合である。接続界面から、Ｃｕ－Ａｌ化合物２１が遊離して、接続界面にはＣｕ－Ｓｎ化合物２３が生成している。これは、接続の早い段階では接続界面に供給できるＡｌが多く存在するためＣｕ－Ａｌ化合物２１が形成するが、接続が進むにつれて、化合物を形成するＡｌが不足するためにはんだ接続時の対流等で界面からＣｕ－Ａｌ化合物２１が遊離してしまうためである。すなわち、Ａｌ含有率１０ｍａｓｓ％未満の接続材料を用いる場合、耐熱性の高いＡｌ－Ｘ系化合物を有する接続界面を得るために、接続条件を短時間にする、接続温度を低温化するといった調整が必要になることを示している。したがってＡｌ含有率を１０ｍａｓｓ％以上とすることにより、幅広い接続条件に対応した接続材料とすることができる。また、Ａｌ含有率を１０～４０ｍａｓｓ％とすることにより、これまで用いられてきた一般的なＳｎ－Ａｇ系はんだに対して、１５％～４０％接続材料を軽量化することができる。
　Ｓｎ－Ａｌ系合金層１３がＳｎ－１０～４０Ａｌ　ｍａｓｓ％であることが望ましい。
　これによって、より軟質な接続材料にすることができる。一般的に、合金を構成する元素が多くなると、析出硬化、固溶強化などによって、合金が硬くなる。パワー半導体素子等の脆性材料を接続する場合、接続材料がより軟質である方が望ましい。
　Ｓｎ－Ａｌ系合金層１３がＺｎを０．０１～９ｍａｓｓ％含んでいることが望ましい。
　Ｓこれにより、はんだの固相線温度を低下させ、最大で約２００℃まで低くすることができる。Ｓｎ－Ａｌ２元系合金の場合、固相線温度が約２３０℃に比べて、約３０℃固相線温度が低いため、接続後の冷却によって生じる残留応力を低減することができる。更に、Ｓｎ－Ａｌ－Ｚｎ３元系は、脆弱な金属間化合物を形成しない合金系であるので、接続部の信頼性を確保できる。また、Ｚｎを主成分として含む場合においても、接続界面にはＡｌ－Ｘ系金属間化合物を形成することができる。Ｚｎ含有率が９ｍａｓｓ％より高くなった場合、Ｚｎが接続材料の濡れ性、耐湿性を損なう恐れがある。
　Ｓｎ－Ａｌ系合金層１３がＩｎを０．０１～７ｍａｓｓ％含んでいることが望ましい。
　これにより、固相線温度を低下させ、最大で約２００℃まで低下させることができる。また、Ｉｎを成分とした場合、Ｉｎが母相であるＳｎ中に固溶するため、母相を固溶強化することができる。更に、Ｓｎ－Ａｌ－Ｉｎ３元系は、脆弱な金属間化合物を形成しない合金系であるので、接続部の信頼性を確保できる。また、Ｉｎを主成分として含む場合においても、接続界面にはＡｌ－Ｘ系金属間化合物がを形成することができる。Ｉｎの含有率が７ｍａｓｓ％以上となった場合、固相線温度が２００℃未満となりはんだの界面反応性が高まるため、１７５℃以上の耐熱性を得るのが難しくなる。
　Ｓｎ系層１１ａのＳｎ含有率が９５～１００　ｍａｓｓ％であることが望ましい。
　これにより、表面に亀裂等発生させること無くクラッド圧延もしくは加圧成形ができ、Ｓｎ－Ａｌ系合金層と良好な金属接合が得られる。表面のＳｎ層１１ａは中央のＳｎ－Ａｌ合金層１３に対して薄く形成する必要があるため、より高い加工性が望まれる。Ｓｎ中に含有率５ｍａｓｓ％より多くの第２元素が存在する場合、Ｓｎ中に析出物が析出する、あるいはＳｎ中に固溶することによって加工性が低下する恐れがある。中央のＳｎ－Ａｌ系合金層１３に前述のＺｎ，Ｉｎなどの第３元素が多く存在した場合、加工性が低下して圧延時に破断したとしても、最表層のＳｎ系層１１ａで封止されているため、特に接続性に影響は与えない。一方、最表層のＳｎ系層１１ａが破れた場合、加工によりＳｎ－Ａｌ系合金層１３表面のＡｌ酸化物の膜を破壊した箇所が、再度酸化してＡｌ酸化物を形成することになり、濡れ性を損なう可能性がある。
　Ｓｎ－Ａｌ系合金層１３とＳｎ系層１１ａの全界面に存在するＡｌ酸化物残存界面の割合が２５％以下であることが望ましい。
　これによって、Ｓｎ－Ａｌ系合金層１３とＳｎ系層１１ａの全界面に存在するＡｌ酸化物残存界面の割合が２５％以下にすることで、濡れ性を阻害することなく、接続ができる。接続材料作製時の加工量が小さい場合、中央部のＳｎ－Ａｌ系合金１３表面のＡｌ酸化物の膜が破れても、破れた膜が界面に残ることで、Ｓｎ－Ａｌ系合金層１３と表面のＳｎ系層１１ａの金属接合を妨げる。Ａｌ酸化物残存界面の割合が２５％より多い場合、未濡れおよびボイドにより、接続部の約２０％が未接続となる。
　Ｓｎ－Ａｌ系合金箔の上下にＳｎ系合金箔を重ねて最終加工度８０％以上でクラッド圧延または加圧成形することが望ましい。
　これによって、最終加工度８０％以上の接続材料にすることで、未濡れ、ボイドが少ない接続ができる。最終加工度とは、圧延および加圧成形前の材料厚さが接続材料として成形された際にどの程度の厚さまで加工されたかを示す指標である。成形前後で厚さが変わらない場合に最終加工度は０％、１０分の１の厚さになった場合、最終加工度を９０％と表す。接続材料の最終加工度と材料内の未接続割合の関係では、最終加工度が低いほど、接続材料内の未接続割合が増加する。この未接続部は、接続材料として部材を接続した場合に未濡れおよびボイドの原因となる。最終加工度を８０％以上にすることで、接続部の未接続割合を２０％以内にすることができる。
　半導体素子と基板とのはんだ接続部のＳｎ含有率が６０～９０ｍａｓｓ％、Ａｌ含有率が１０～４０ｍａｓｓ％であることが望ましい。
　これによって、耐熱性が高く、軽量な半導体装置が得られる。ＳｎとＡｌを主成分とすることで、はんだ接続部に脆弱な金属間化合物のない接続ができる。Ｓｎが６０％未満の場合、接続部の軟質さが低下し、熱応力発生時に十分な応力緩衝ができない。また、Ｓｎ含有率が９０％より高い場合、Ａｌ含有率が１０ｍａｓｓ％未満となるため、１５０℃以上の高温下において界面反応を抑制するＡｌ－Ｘ系化合物を形成することが難しくなる。Ａｌ含有率が４０ｍａｓｓ％より高い場合は、本発明の接続材料では形成することができない。
　（実施例１－２０）以下、本発明をパワー半導体モジュールに適用した実施例について説明する。
　表１の仕様である最表層のＳｎ系合金層２０μｍ、中央層のＳｎ－Ａｌ系合金層が１０0μｍの厚さ１４０μｍのクラッド材２を作成した。まず、ＡｌとＳｎとを表１の仕様の割合で加熱溶融させ、Ｓｎ－Ａｌ系合金層を作成し、Ｓｎ－Ａｌ系合金層の両面にＳｎ系層を設け、クラッド加工を行なうことでクラッド材２を作成した。
　そして作成したクラッド材２を基板３上に置き、その上に１０ｍｍ×１０ｍｍ．のパワー半導体素子６を積層し、素子上におもしを置き、Ｈ2還元雰囲気中、３００℃５ｍｉｎ．で接続を行った。ワイヤボンディング１を行った素子付基板を厚さ２００μｍのＳｎ－Ａｇ系はんだで支持部材５に接続し、ケースを取り付けて、接続部周辺にゲルを注入して硬化させ、図１に示すような半導体装置を作製した。クラッド材２以外は、従来の半導体装置と同一である。
　この半導体装置接続工程に用いた素子接続材料のＳｎに対する比重、素子接続部の接続面積、半導体装置を１７５℃で１０００ｈ保持したときの接続部の空隙生成状況を調査した結果を表１に示す。素子接続面積については、接続面積が素子面積に対して９０％以上の場合を○、９０％未満の場合を×とした。また、１７５℃１０００ｈ保持に関しては、１０００ｈ保持後に接続界面の断面観察を行い、素子接続界面において空隙が生成しなかったものを○、空隙が生成したものを×とした。
　表１のように、実施例１から２０において、Ａｌ含有率が高いほど、Ｓｎに対する重量比が軽くなった。接続面積においては、何れの実施例の場合も素子面積に対して９０％以上の接続面積が得られた。１７５℃１０００ｈ後の接続部の空隙生成状態について確認したところ、何れの実施例においても接続部に空隙は形成されていなかった。以上のことから、本発明を用いることで、濡れが確保でき、耐熱性が高く、軽量化が可能なことが明らかとなった。なお、上記では全体構造を編み線状導体と半導体素子、半導体素子と基板の接続を別々に接続するプロセスについて述べたが、半導体素子、クラッド材、基板、はんだ、支持部材を積層した後、一度のプロセスで接続しても良い。
Figure JPOXMLDOC01-appb-T000001
（比較例１、２）
　基板上に、厚さ１５０μｍのＳｎ－３．５ＡｇあるいはＳｎ－０．７Ｃｕはんだ箔を置き、その上に１０ｍｍ×１０ｍｍ．のパワー半導体素子をおき、更に素子上におもしを置き、Ｈ2還元雰囲気中、３００℃５ｍｉｎ．で接続を行った。ワイヤボンディング１を行った素子付基板を厚さ２００μｍのＳｎ－Ａｇ系はんだで支持部材５に接続し、ケースを取り付けて、接続部周辺にゲルを注入して硬化させ、半導体装置を作製した。
　上記の実施例１から２０と同様に、Ｓｎに対する重量比および接続面積、１７５℃１０00ｈ後の接続界面への空隙生成状況を調査した。その結果、表２のように、重量比はＳｎと同等、接続性は何れの場合も素子面積に対して９０％以上の濡れを確保することができた。一方、１７５℃１０００ｈ保持後の素子接続部の接続界面を観察したところ、図２のような空隙が接続界面に生成していた。
（比較例３－６）
　厚さ１５０μｍの表２に示すはんだ箔を用いて、素子を接続し、比較例１、２と同様の工程で半導体装置の組立を行った。しかしながら、何れの比較例においても、表２のように９０％未満の接続面積となった。特に比較例４については、ほとんど濡れている箇所が無かった。良好な接続が得られなかったため、１７５℃１０００ｈ保持による耐熱性は実施できなかった。
Figure JPOXMLDOC01-appb-T000002
　実施例では半導体素子と基板とを接続する接続材料を用いて説明したが、接続する対象はこれに限られず、接続端子やリードなど他の部材でもよい。
１　Ａｌワイヤ、２導電性接合材（はんだ）、３　基板、４　はんだ、５　支持部材、６　パワー半導体素子、７　はんだ、８　金属間化合物、９　導電性接合材、１１　Ｓｎ系はんだ、１１ａ　Ｓｎ系層、１１ｂ　Ｓｎ成分、１２　Ａｌ成分、１３　Ｓｎ－Ａｌ系合金層、１４　Ｃｕ部材、　１５　Ｎｉめっき、１６　クラッド材、２１　Ｃｕ－Ａｌ化合物、２２　Ｎｉ－Ａｌ化合物、２３　Ｃｕ－Ｓｎ化合物、１０１　空隙。

Claims (14)

  1. 　Ａｌ含有率が４０ｍａｓｓ％以下のＳｎ－Ａｌ系合金層と、
    　前記合金層の最表面に設けられたＳｎ系層とを備えたことを特徴とする接続材料。
  2. 　請求項１記載の接続材料において、
    　前記Ｓｎ層は、
    　前記Ｓｎ－Ａｌ系合金層の主面に設けられた第一のＳｎ層と、
    　前記第一のＳｎ系層とは反対側の前記Ｓｎ－Ａｌ系合金層の主面に設けられた第二のＳｎ層とを備えたことを特徴とする接続材料。
  3. 　請求項１または請求項２において、
    　前記Ｓｎ－Ａｌ系合金層と前記Ｓｎ系層とはクラッドまたは加圧成形により接続されていることを特徴とする接続材料。
  4. 　請求項１記載の接続材料において、
    　前記Ｓｎ－Ａｌ系合金層のＡｌ含有率が１０～４０ｍａｓｓ％であることを特徴とする接続材料。
  5. 　請求項１記載の接続材料において、
    　前記Ｓｎ－Ａｌ系合金層がＳｎ－１０～４０Ａｌ　ｍａｓｓ％であることを特徴とする接続材料。
  6. 　請求項４記載の接続材料において、
    　前記Ｓｎ－Ａｌ系合金層がＺｎ含有率が０．０１～９ｍａｓｓ％であることを特徴とする接続材料。
  7. 　請求項４記載の接続材料において、
    　前記Ｓｎ－Ａｌ系合金層がＩｎ含有率が０．０１～７ｍａｓｓ％であることを特徴とする接続材料。
  8. 　請求項１から７のいずれかに記載の接続材料において、
    　前記Ｓｎ系層のＳｎ含有率が９５～１００　ｍａｓｓ％であることを特徴とする接続材料。
  9. 　請求項１から８のいずれかに記載の接続材料において、
    　Ｓｎ－Ａｌ系合金層とＳｎ系層の全界面に存在するＡｌ酸化物界面の割合が２５％以下であることを特徴とする接続材料。
  10. 　請求項１から６記載の接続材料において、
    　Ｓｎ－Ａｌ系合金箔の上下にＳｎ箔を重ねて最終加工度８０％以上でクラッド圧延したことを特徴とする接続材料。
  11. 　第１の部材と、第２の部材と、前記第１の部材と前記第２の部算とを接続するはんだ接続部とを備えた半導体装置において、
    　前記はんだ接続部のＳｎ含有率が６０～９０ｍａｓｓ％、Ａｌ含有率が１０～４０ｍａｓｓ％であることを特徴とする半導体装置。
  12. 　前記第１の部材は半導体素子であり、前記第２の部材は、基板またはリードであることを特徴とする半導体装置の製造方法。
  13. 　Ｓｎ層にＡｌ層を加熱溶融させ、Ａｌ含有率が１０～４０ｍａｓｓ％のＳｎ－Ａｌ層を形成する工程と、
    　前記形成したＳｎ－Ａｌ層の表裏面にそれぞれＳｎ層をクラッドするまたは加圧成形により形成する工程とを含む接続材料の製造方法。
  14. 　請求項１乃至１０のいずれかに記載の接続材料を、第１の部材と第２の部材との間に設ける工程と、
    　前記接続材料を加熱し、前記第１の部材と前記第２の部材とを接続する工程と、
    　を含む半導体装置の製造方法。
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